Method of manufacturing a grinder or hone having fine cushiony surfaces



United Sites 3,092,476 METHOD OF MANUFACTURING A GRINDER OR HONE HAVINGFINE CUSHIONY SURFACES Yoshio Yatabe, 1 l-chome Jujo-nakahara Kita-ku,Tokyo, Japan No Drawing. Filed Sept. 25, 1959, Ser. No. 842,361 Claimspriority, application Japan Sept. 27, 1958 2 Claims. (Cl. 51-293) Thisinvention relates to a high finish grinder or hone characterized bynumerous fine cushiony surfaces of polymeric materials distributedaround the uniformly bound abrasives and to the manufacturing methodthereof. The object of the invention is to oifer such a grinder or honethat the shocks or impulses against the work surface to be ground due tothe mechanical vibrations during grinding can be prevented to produce anextremely smooth and accurate surface, and also to provide an easy andsimple method to manufacture such a grinder or hone.

Extreme smoothness and accuracy like an optical flat is generally mostdesirable in a grinding operation. However, such a surface is verydifiicult to obtain even by the modern super-finishing, lapping, honing,polishing, etc. The only method to realize this is so-called precisionlens-polishing process by means of a .pitch lap which is applied forpolishing optical glass or crystal. However, such a lapping method isconfined to the special materials as aforementioned, and it is notapplicable for common metals which are strong enough and useful forenergy transmissions. The only processing for such a high finish formetals is the method applied for finishing block gauges, for whichextreme skill and patience are required, of course. The basic idea ofthe processing for block gauges is to copy the smoothness and flatnessof the highly finished surface of the lap onto the work surface.However, generating such a lap surface and maintaining its accuracy arealmost impossible except by an expert of more than ten years experience.

By the grinder or hone of the present invention, any metal can befinished to the extreme extent of smoothness and accuracy without highskill or long experience. By the grinder or hone of the invention,contrary to the aforementioned method for block gauges, both smoothnessand flatness can be attained simultaneously by means of thediscontinuously spaced abrasives of O.51,u. to several hundreds meshsize.

In the conventional mechanical working processes wheel or hone, scraper,lap, etc. are actuated with relative displacements or motions withregard to the work materials. Therefore, periodic or non-periodicvibration cannot be avoided during the operations. In other words, notonly the tangential motion along the work surface which is essential tomachining, grinding, lapping or polishing action, but the verticalmotion harmful to the work surface also takes place in usual finishingoperations. The vertical motion to the work surface is conspicuouslydetrimental to accuracy or smoothness of the work surface. For example,in a grinding machine, the perfect revolution of the wheel spindle(5000-6000 rpm.) entirely free from any vibration cannot be expected bythe best fit between the wheel spindle and the hearing as well as by thebest balance of the rotating system. So that, a conventional grinder orhone of vitrifide, silicate, resinoid, rubber, synthetic resin or thelike bond directly contacts the work surface with the hard abrasives andgrinds the work surface with the above mentioned inevitable vibrationsto cause the vertical shocks or impulses against the work surface.

In the conventional grinder or hone, the function of bond such asvitrifide, rubber, synthetic resin or the 3,092,47fi Patented June 4,1963 like is merely to bind numerous abrasives, and it does not implythe aforementioned cushiony action of abrasives against the vibratoryshock.

As widely known, if the bonding strength of a bond, which is expressedby the term of hardness or grade, is adequate, the abrasives having wornout or dull edges due to the numerous grinding actions are destined todrop off or to cause cleavage automatically to expose the new and sharpcutting edges which are essential to the efficient grinding action. Thisis called self-dressing action of a grinder or hone.

Although the above explanation is very reasonable as far as normal orconventional grinders or homes are concerned, the other type of grinderor hone than the conventional must be required for a better performancein the case where metal removal is very slight, so that the grindingactions of the abrasives are confined to the extremely thin layer of thework surface as in a precision fine grinding operation.

Generally speaking, grinding abrasives are much harder than usual workmaterials, so that abrasives will not be scratched or abraded by workmaterials through the same process as that the materials are scratchedor ploughed by the abrasives. Nevertheless, the abrasives of grinder orhone actually drop off during the grinding action. This seems to bebecause of that the abrasives plunged into the work material have atendency to be captured and broken by the material or fractured by thevibratory shocks or impulses due to the rotation of the grinder. Thus,the surface layer of the grinder or bone drops off one after another andat the same time the work surface is seriously damaged or scratched dueto the reaction. Apparently this is detrimental to a precision surfacefinish.

The grinders or homes of the present invention can easily effect muchsuperior finishes in smoothness, fiatness and accuracy to those obtainedby conventional ones. In the grinder or hone of the present invention,the particles of synthetic resin polymer or copolymer are uniformlydistributed in the structure of abrasives bound together tightly.Generally as a grinder or hone wears out very slowly by the relativemotions between the grinder or hone and the work material while they arein contact, the tops of the distributed polymer particles are exposed tothe grinder or hone surface, said exposed tops of the particles makingan envelope surface as a whole, wherein the grinding abrasives areclosely stuck around the polymer particles. It appears as if themountains of polymer particles having the exposed flat tops aresurrounded by the abrasives at the middle parts of the mountains. Whensuch a grinding surface makes frictional contact with a work material tobe ground or polished, the exposed tops of the polymer particles touchthe work surface first, and then, when the grinding pressure isincreased, the grinding abrasives located just behind the exposed fiatsurfaces of the polymer particles come in contact with the work surfaceby the minute elastic deformations of the polymer particles so that asoft and desirable grinding action can be performed by the friction orabrasion of the grinder or hone. In this process, the exposed elastictops of polymer particles act as a cushiony absorber of the inevitablevibratory impulses or shocks during grinding. As understood by the aboveexplanation, the contact between the grinder or hone and the worksurface is so soft and light that the hammering action resulting into arough finish can be decreased considerably. Therefore, by the grinder orhone of the present invention, ultra-finish up to 0.002 (2 x 10-6 mm.)and extreme dimensional accuracy like that of an optical glass can beobtained.

In accordance with this invention, the precision of flatness attained bythe ground surface being such that the roughness of the surface attainedwas 0.002; and the Newton rings became monochromatic. In other words, inaccordance with this invention, a metallic surface can be finished to adegree comparable to that of an optical glass.

In accordance with this invention, grinding abrasives, of which gritsize is to be selected in accordance with the objects of grinding in therange from (LS-1 to several hundreds mesh, are properly bound by asynthetic resin. Numerous polymer particles which are the same or largerin size as said abrasives, i.e., several tens to several hundreds mesh,are distributed in said structure consisting of the abrasives and theresin bond. The polymer particles are manufactured by such mechanicalprocess as crushing and the like, or by emulsion or suspensionpolymerization.

And moreover, by the use of the grinder or hone of the presentinvention, a metallic surface was finished up to 0.002;.t in surfaceroughness and in flatness to such an extent that the Newton rings becamealmost monochromatic.

The manufacturing method of the grinder or hone of the invention is asfollows:

Grinding abrasives and hue particles of a synthetic resin type polymermixed in together in a specific ratio are put into a metallic mould andhot-pressed to be bound together into a shaped structure, one or moresynthetic resin monomers different or the same as the said syntheticresin, which are mixed together into a single phase by adding aplasticizer or without adding it, or are somewhat polymerized to be alow grade polymer for each case above mentioned, being absorbed intosaid prosintered abrasives and polymer particles or not absorbed to betempered, and finally the polymerization is completed by heating orother means to be tempered and stabilized.

The present invention has such merits as high productivity and low costbecause of the speedy circulation of the metallic mould. Besides,according to the invention, one can control the properties of thegrinder or hone or improve its quality freely by means of addingmonomers, plasticizer, low grade polymer, polymerization accelerator,etc. after the preliminarily sintered grinder or hone is accuratelymachined or formed.

'In manufacturing conventional grinders or homes, a great amount of carehas been required in mixing the abrasives and bonds uniformly, but inthe present invention there is not such a trouble at all because thebonding process of the abrasives can be eflectively performed whilemaintaining the polymer particles distributed around the abrasives undera definite structure.

If higher grinding efliciency is desired, the amount of the abrasivesshould be as large as possible While keeping the amount of polymerparticles to bind said abrasives as small as possible.

Even though the polymer particles are softened by heating to have themaximum fluidity, it cannot be expected that their bonding strength isexerted on the abrasives located Within the distance of two or threetimes diameter of said polymer particles, because there is a certainlimit in the range of the bonding strength or ability of said polymerparticles at the stage of pre-sintering. If such a grinder or honeinsufiicient in bonding strength as a whole is applied to an actualoperation, it will not be able to stand the grinding pressure and Willbe broken down. Therefore, other treatments are often needed to increasethe bonding strength enough to stand various grinding pressures afterthe hot-pressing process which is regarded as a kind of pre-sintering.

In the case of the present invention, as an example the pre-sinteredgrinding Wheel or hone is dipped into a monomer, then taken out to befurther heated for the purpose of polymerizing the monomer afterremoving of superfluous drops of the monomer. In this case, the

4 monomer enters into the deepest spots through the capillary gaps amongthe grinding abrasives while dissolving the surfaces of the polymerparticles distributed to become one body or phase, and the bondingprocess of the abrasives is completed by being solidified as thepolymerization progresses.

Although in the process of dip-tempering only one monomer is used in theforegoing example, two or more types of monomers may be used orplasticizer also may be added if desired. Furthermore, a polymerizingaccelorator is effective to speed up the polymerization and to attainhigher productivity.

Porous products can be easily obtained, if desired, by addingfoam-forming agents, or. otherwise by rapidly raising up the temperaturewithout adding the above.

The monomer can be used in the state of a low-grade polymer if lowviscosity by being somewhat polymerized in advance is convenient for thetempering process.

For a better' understanding, the following examples shall be given as amore concrete illustration of the nature of this invention.

Example 1 5 gr. silicon carbide (#1000) and 2 gr. of particles ofpolymethyl methacrylate are mixed up uniformly, put into a metallicmould, heated up to 140 C., cooled down to room temperature under thepressure of about 100 kg./crn. and thereafter taken out of the metallicmould. The material thus pre-sintered is dipped into monomethylmethacrylate, taken out after impregnated with the monomer, from whichthe superfluous drops of the monomer are removed, and then polymerizedand solidified in a thermostatically controlled bath of 50 to 100 C. tobe the final product.

Example 2 6 gr. cerium oxide and 3 gr. copolymer particles of methylmethacrylate and butylmethacrylate are presinter'ed as in Example 1.Thus pre-sintered material is dipped into low grade polymer produced bymixing and dissolving 5 cc. of monomethyl methacrylate, 5 ,cc. ofmonobutylacrylate, 5 cc. of dibutyl phthalate and 0.1 gr. of benzoylperoxide, and heated to be polymerized in a thermostatically controlledbath of C. after eliminating the superfluous drops of the low gradepolymer. In this process, the desirable temper can be performed rathereasily by controlling the dipping time, the viscosity of monomericlow-grade polymer, etc.

As to grinding abrasive, diamond powder, boron carbide, silicon carbide,aluminum oxide, other metallic oxides, etc. can be applied regardless oftheir grit size.

The polymer particles may be either spherical or formless, and bothpolymeric synthetic resins such as a methacrylate resin, styrol resin,vinyl resin, etc. and condensation synthetic resins such as polyesterresin, phenol formaldehyde resin, urea formaldehyde resin, etc. areapplicable as the material.

The compatibility between the polymer particles and monomeric low-gradepolymer used in tempering is not necessarily essential, but the poorcompatibility can yield a special effect upon the product.

The compatibility of the plasticizer is also not so important;Therefore, the ranges for selecting polymer, monomer and pl-asticiz'er,the latter two of which are used for tempering, are so wide that almostany of synthetic resins can be used.

Since it is apparent that many changes and modifications can be made inthe above described details without departing from the nature and spiritof the invention, it is to be understood that the invention is not to belimited thereto except as set forth in the appended claims.

What is claimed is:

1. Method of preparing a grinder or bone having a cushiony surface,which comprises mixing abrasive particles and particles of a syntheticresin selected from the group consisting of vinyl resins, polyesterresins, and urea formaldehyde resins, putting said mixture into a mould,heating said mixture under pressure in said mould in order to obtain apre-sintered moulded article, dipping said pre sintered, moulded articleinto a mixture of a liquid monomeric material selected from the groupconsisting of vinyl monomers, polyester monomers nad urea formaldehydemonomers and polymerization catalyst therefore, and then heating saiddipped article to completely polymerize said monomeric resin.

2. Method according to claim 1 wherein said synthetic resin is selectedfrom the group consisting of polymethyl methacrylate and a copolymer ofmethyl methacrylate and butyl methacrylate; and said monomeric syntheticresin is an alkyl methacrylate.

References Cited in the file of this patent UNITED STATES PATENTS2,117,513 Scutt May 17, 1938 2,246,898 Sayre June 24, 1941 2,256,618Kistler et al. Sept. 23, 1941 2,308,854 Barnes Jan. 19, 1943 2,377,995Coes June 12, 1945 2,774,108 Wyllie Dec. 18, 11956

1. METHOD OF PREPARING A GRINDER OR A HONE HAVING A CUSHIONY SURFACE,WHICH COMPRISES MIXING ABRASIVE PARTICLES AND PARTICLES OF A SYNTHETICRESIN SELECTED FROM THE GROUP CONSISTING OF VINYL RESIN, POLYSTERRESINS, AND UREA FORMALDEHYDE RESIN, PUTTING SAID MIXTURE INTO A MOULD,HEATING SAID MIXTURE UNDER PRESSURE IN SAID MOULD IN ORDER, TO OBTAIN APRE-SINTERED MOULDED ARTICLE, DIPPING SAID PRESINTERED, MOULDEDARTICLEINTO A MIXTURE OF A LIQUID MONOMERIC MATERIAL SELECTED FROM THEGROUP CONSISTING OF VINYL MONOMERS, POLYESTER MONOMERS NAD UREAFORMALEDHYDE MONOMERS AND POLYMERIZATION CATALYST THEREFORE, AND THENHEATING SAID DIPPED ARTICLE TO COMPLETELY POLYMERIZE SAID MONOMERICRESIN.